C1 is set to DR400, ISO800 with ISO bracketing set to ±1 (ISO400/800/1600 at the same time)
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C2 is set to DR200, ISO200 with ISO bracketing set to ±1 (ISO100/200/400 at the same time)
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When in doubt of expecting ORBs in my picture - with either night or day shots - I use C1 for night and C2 for day shots. Why? Well at this time it is widely known that a higher ISO value will lead to less ORBS but more noise. When you use ISO bracketing you have three pictures of the same subject. One with ORBS and less noise, One without (or with less) ORBS but with more noise and one in between. In Post-processing (Photoshop) you can easily balance between noise and ORBS by making three layers of these pictures and using the eraser tool. You get the picture! A major disadvantage of this method is it takes more time. Both when you shoot your picture (the FUJI X10 has to store three images) and in post-processing. I use a Sandisk 95MB/s SDXC wich cuts down storing time. I know it is not ideal but I find it axeptable. Good luck with experimenting!